Follow-up re the AC pressure switch.
A little reading found the switch in my 1984 & 85 300D cars is simply a low-pressure cut-off switch. I found that many 1976 - 2011 M-B (ex. 84-93 190E) have a binary switch which also gives a high-pressure cut-off. Apparently the same 3/8-24 thread w/ corner O-ring seal, and same male spade connectors (56 terminal). But, P-P lists 9.5 mm thread for the OE switch (which is 3/8"). Switches off at <2.1 bar or >24 bar (30.5 & 348 psig). I would prefer a lower HP cut-off ~280 psig, but hopefully that will still protect the clutch from slipping. PN's are Behr Hella 351022011 or M-B 124-820-8310. I bought 2 (~$10) and will install in my cars on a very cold day this winter, to avoid losing much refrigerant.

BTW, there are also "trinary" pressure switches. These have a 3rd terminal for the electric fan. It shorts to ground to turn on the fan relay at higher pressure. But that would require wiring changes. In a similar vein, Rollguy showed how to rewire your radiator fan relay so it turns on with the AC clutch. The downside being that the fan would run even at highway speeds when it isn't needed.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans